U.S. patent application number 11/244655 was filed with the patent office on 2007-04-12 for method and apparatus of image buffer compression for display device.
Invention is credited to Chih-Ta Star Sung.
Application Number | 20070080971 11/244655 |
Document ID | / |
Family ID | 37910688 |
Filed Date | 2007-04-12 |
United States Patent
Application |
20070080971 |
Kind Code |
A1 |
Sung; Chih-Ta Star |
April 12, 2007 |
Method and apparatus of image buffer compression for display
device
Abstract
A method and apparatus for reducing the density of a frame
buffer image for display device is presented. The source image is
compressed before storing into a temporary frame buffer and
decompressed before displaying in a display device. When a new
object is to be display into the previous frame, the starting and
ending position of each line and segment which the new object
pixels reside are calculated and the corresponding segments of
pixels are decompressed to be concatenated with the new object
pixels and re-compressed before storing into the frame buffer.
Inventors: |
Sung; Chih-Ta Star; (Glonn,
DE) |
Correspondence
Address: |
Chih-Ta Star Sung;RM. 308, BLD.52
NO. 195, CHUNG HSING RD.
SEC. 4 CHU TUNG TOWNSHIP
HSINCHU COUNTY
310
TW
|
Family ID: |
37910688 |
Appl. No.: |
11/244655 |
Filed: |
October 6, 2005 |
Current U.S.
Class: |
345/545 ;
345/555; 375/E7.096 |
Current CPC
Class: |
H04N 19/427 20141101;
G09G 2360/18 20130101; G09G 3/20 20130101; G09G 2340/02
20130101 |
Class at
Publication: |
345/545 ;
345/555 |
International
Class: |
G09G 5/36 20060101
G09G005/36; G06T 9/00 20060101 G06T009/00 |
Claims
1. A method of frame buffer image compression and decompression for
display device, comprising: compressing a group of pixels of the
image source; saving the compressed group of pixels into a first
temporary storage device; before displaying, decompressing a group
of compressed pixels of the compressed data; and sending the
decompressed pixels to a second temporary storage device for
driving out to a display device.
2. The method of claim 1, wherein the image source is comprised of
at least one of Red, Green, Blue color element.
3. The method of claim 1, wherein the image source is comprised of
at least one of Y, Cr, Cb or Y, U, V element.
4. The method of claim 1, wherein the group of pixels as a
compression unit is a frame of image.
5. The method of claim 1, wherein the group of pixels as a
compression unit is a line of pixels.
6. The method of claim 1, wherein the group of pixels as a
compression unit is a segment of pixels.
7. The method of claim 1, wherein the decompressed group of pixels
are sent out to let the source drivers drive the corresponding
color elements to the display device.
8. The method of claim 1, wherein a source driver drives three
color elements out to the display device.
9. A method of frame buffer image compression for display device,
when a new object of an image is sent to be displayed together with
previous frame of image, this method efficiently reduces the
density of storage device and bandwidth requirement of transmitting
by procedures, comprising calculating the starting and ending
points of each line of pixels of the new object; decompressing the
corresponding segment of pixels of each line of the latest image
saved in the frame buffer on which the pixels of the new object
will reside; Concatenating pixels of the decompressed image and the
new object of pixels within corresponding segments which have
pixels of new object; and re-compressing the corresponding segment
of pixels of each line of the existing image on which the pixels of
the new object will reside;
10. The method of claim 9, wherein a new object is comprised of a
group of pixels.
11. The method of claim 10, wherein a group of pixels of the new
object is comprised of pixels distributed in at least one line or
one segment.
12. The method of claim 9, wherein when decompressing the
corresponding segment of pixels, the procedure ends in the pixel
where the new object starts and the rest of pixel till the end of a
segment are replaced by pixels of the new object.
13. The method of claim 9, wherein when decompressing the
corresponding segment of pixels, the pixels of the new object which
fall on the beginning of a new segment replace pixels of the
decompressed pixels in the former section of a segment.
14. The method of claim 9, wherein the segments with no new object
residing will be left compressed format.
15. An apparatus of frame buffer image compression and
decompression for display device, comprising: a compression engine
with a first speed of clock rate which takes a group of pixels of
the image source and compresses into a smaller amount of pixel
data; a timing control unit which determines the timing of driving
out the corresponding pixels onto the display device; another
compression and decompression engine with a second speed of clock
rate to recover the existing segment pixels and merging new object
pixels to form a new line and re-compress the new line and save it
back to the frame buffer; a decompression engine which recovers a
group of pixels of stored in the frame buffer to be driven out to
the display device; gate driver circuit which select the row of
display pixels; and source driver circuit with each pixels having
Red, Green and Blue element to be sent out to be displayed.
16. The apparatus of claim 15, wherein the timing control unit
calculates the timing of driving out the corresponding pixels color
elements of each row by sending signal to the gate drive, the
source driver and the frame buffer of image regarding the right
timing and location of frame pixels to be displayed.
17. The apparatus of claim 15, wherein at least one temporary
segment pixel buffer is implemented for intermediately saving the
decompressed pixels of corresponding segments.
18. The apparatus of claim 15, wherein the compression engine is
used to compress the decompressed and concatenated segment of
pixels with new object.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to image
compression/decompression, and more particularly relates to the
temporary image compression/decompression for display device which
reduces the density requirement of the storage device.
[0003] 2. Description of Related Art
[0004] The sharp quality of Liquid Crystal Display, LCD devices
coupled with manufacturing cost reduction in the past years have
driven mass production of the LCD related display products in wide
applications including display panels of mobile devices like
digital TV panel, PC screen panel, portable DVD player, digital
still camera (DSC), digital video recorder (DVR), mobile phone,
electronic dictionary, telephony panel, video phone, . . . etc.
[0005] As shown in FIG. 1, most display systems are comprised of
the three main devices: display timing controller 11 and display
driver 12 which in many of the latest designs include a frame
buffer 13 and a display panel 14. Since display driver, for
example, the LCD driver resides a lot of MOS transistors which need
to conduct relatively high voltages compared to common used power
supply voltage (ex. 3.3V in 0.35 um process) of MOS process, to
avoid device breakdown effect, the channel length of the drivers
are much longer than regular MOS devices hence dominate large die
area. In multimedia era, larger and larger image are integrated
into the frame buffer which is commonly comprised of SRAM memory
array within a display driver which makes the die area of a display
driver even larger. The larger the die area, the lower the yield a
chip can obtain and the higher power it will consume.
[0006] Therefore, it is beneficial to reduce the required amount of
storage devices of the on-chip reference frame buffer to further
reduce the cost and power consumption.
SUMMARY OF THE INVENTION
[0007] The present invention is related to a method and apparatus
of the frame buffer image compression for display device, which
plays an important role in significantly reducing the required
storage device density.
[0008] The present invention of the frame buffer image compression
includes procedures and apparatus of compressing the frame buffer
image and saved in a storage device and decompressing the frame
buffer image data and sending the recovered image to the display
drivers to be displayed.
[0009] According to an embodiment of the present invention of the
frame buffer image compression, when a new object is to be inserted
into the existing frame of image to be displayed, the starting and
ending position of each line of new object will be calculated and
the corresponding segment of the existing image is identified and
recovered to be raw data to let the pixels of new object insert to
the right position and re-compress the concatenated pixels.
[0010] According to an embodiment of the present invention of the
frame buffer image compression, a part of an image is compressed
and saved into the frame buffer which reduces the requirement of
density significantly.
[0011] According to an embodiment of the present invention of the
frame buffer image compression, when a new object is sending to the
frame buffer, the engine with higher speed clock rate is turned on
to decode the corresponding segment with the new object,
concatenating the new pixels and re-compress the corresponding
segments.
[0012] According to an embodiment of the VLC coding algorithm of
this invention of frame buffer image compression, only the
"Quotient" and "Remainder" are coded with the "Divider" implicitly
done by prediction.
[0013] It is to be understood that both the foregoing general
description and the following detailed description are by examples,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a prior art of a display system having a
driver with a frame buffer comprising of an SRAM.
[0015] FIG. 2 illustrates a prior art of a driver chip with a large
frame buffer, source drivers and gate drivers.
[0016] FIG. 3 depicts the block diagram of the present invention of
the display driver chip of source drivers, gate drivers plus a
frame buffer with image compression and decompression.
[0017] FIG. 4 depicts a method of compression with half line of
pixels as a compression unit.
[0018] FIG. 5 depicts a method of compression with a segment of
pixels as a compression unit.
[0019] FIG. 6 illustrates a case of inserting a new object into a
frame of image including the description of beginning and ending
point of the new object.
[0020] FIG. 7 illustrates the combined image of inserting a new
object into a frame of image.
[0021] FIG. 8 depicts the procedure of inserting a new object into
a frame of image.
[0022] FIG. 9 depicts the procedure of details of inserting a new
object into an existing line of image.
[0023] FIG. 10 illustrates the block diagram of the implementation
of inserting a new object into an existing frame of image to be
displayed.
[0024] FIG. 11 illustrates the apparatus of applying even smaller
frame buffer to store a partial of an image.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The LCD related display device has wide applications
including display panels of mobile devices like digital TV panel,
PC screen panel, portable DVD player, digital still camera (DSC),
digital video recorder (DVR), mobile phone, electronic dictionary,
telephony panel, video phone, . . . etc.
[0026] A display system, said an LCD panel, is like a traditional
TV with the image displayed line by line sequentially. Most prior
art display systems are comprised of the three main devices as
shown in FIG. 1: the display timing controller 11 and display
driver 12 which in many of the latest designs include a frame
buffer 13 and a display panel 14.
[0027] FIG. 2 depicts a prior art of display device driver, said
LCD driver chip which comprised a timing control unit, a frame
buffer, some source drivers and gate drivers. An image source 21 is
received and temporarily saved in a frame buffer 22. In an SoC
(System On Chip) high integration chip design, the frame buffer is
comprised of SRAM (Static Random Access Memory) array for quick
accessing. The timing control unit 28 calculates the time to
display each line of pixels and controls pixels to drive out to be
displayed. The gate drivers 25, 26 comprising some decoders which
decide the row number of display. The gate driver is similar to the
row driver in a memory array which selects the row number to be
accessed in a memory array. Most likely the display starts from
selecting the gate driver from top row down to bottom row
sequentially. The source drivers 23, 24 drive out the pixels with
each pixel column comprising three elements, said Red, Green and
Blue to the display panel, for example, an LCD display panel.
Therefore, the image to be displayed is saved in a frame buffer and
to wait till the right time to start driving out line by line
through the source drivers with the line (row) controlled by the
gate drivers. For easy in design and control, the frame buffer
saves a whole frame of image.
[0028] The larger the display screen (panel) the larger frame
buffer will be required to save the data of pixels. In larger image
size or display panel applications, this invention of frame buffer
compression gains higher efficiency in data reduction. For
instance, the mobile phone with color display of 128.times.128 size
of display needs about 200K bits SRAM with 6-6-6 bits of R,G,B
elements which dominates about 25% of die area of an LCD driver
chip, while in 320.times.240 display resolution, the SRAM size of
frame increases to 1.0M bits which dominates about 60% of an LCD
driver chip with 0.25 um high voltage CMOS process.
[0029] This invention said frame buffer compression of pixel data
reduces die area ranging from .about.15% to 30% depending on the
resolution. Reducing the density of frame buffer and die area gains
another benefit of lower power consumption since power consumption
is linearly proportional to the capacitance loading.
[0030] FIG. 3 illustrates the block diagram of this invention of
the frame buffer compression of the frame buffer for display
device. An image source 31 is sent to be displayed will be firstly
compressed by a compression engine 32 before temporarily saving to
the frame buffer 38 which most likely an SRAM memory array. When
the timing of display reached, the corresponding line of pixels
will be recovered by the decompression engine 39 and feed to the
source drivers 33, 34 to be display onto the display panel 37. The
gate drivers decide the row number for those corresponding row of
pixels to be displayed on the display panel. A timing control unit
300 calculates the right timing of displaying the right line of
pixels stored in the frame buffer, sends signal to the frame buffer
and the decompression engine to inform the status of display. For
instance, send an "H-Sync" signal to represent a new line needs to
be display within a certain time slot. When the decompression
engine receives this signal, it starts accessing the frame buffer
and decompressing the compressed pixel data and recovers the whole
line of pixels and send them to the source driver unit for
display.
[0031] The compression and decompression engine of this invention
of the frame buffer compression of the frame buffer for display
device adopts a whole frame of image pixels as a compression unit,
also adopts a line of image pixels and a segment of image pixels as
a unit of compression. When a frame pixels are defined as the group
of compression unit, a predetermined compression rate, for example,
said 2.0.times.is reached of reducing the frame data rate by a
factor of 2.0. When a half line of pixels is selected as a group of
pixels of compression unit as shown in FIG. 4, the 1.sup.st half
line 41 of pixels is compressed independently from the 2.sup.nd
half line of pixels 42. The compressed 1.sup.st half line 43 and
the compressed 2.sup.nd half line 44 are concatenated to form a
compressed line 45 which is 50% length of the original uncompressed
line. The two half lines of compression can be done in parallel or
in series. In compressing in parallel, the original image should
have a whole line of pixels ready. FIG. 5 depicts another mechanism
of this invention of the frame buffer compression of the frame
buffer for display device which uses smaller number of pixels as a
compression unit called "segment". A segment represent a group of
pixels of a certain length of pixels, for example, said 1/4 or 1/8
of a line pixels. Segment 1, said Seg.1, Seg. 2 to Seg. n 51, 52,
53 are compressed independently and result in the compressed
segments 54, 55, 56 which together form a line of compressed
pixels. A whole frame buffer of pixel can be compressed line by
line with fixed compressed rate of each line or variable
compression rate from line to line and reaches a final fixed
compress rate of a whole frame.
[0032] In some applications, there will be a new object being
displayed together with last image in the frame buffer. For
instance, a frame buffer storing an image of Mr. Mickey, a new
object of a peanut might be sent to shown on his mouse. In this
case, the display panel still keeps displaying the original frame
buffer content of Mr. Mickey and will add new object of a peanut
from a corresponding location.
[0033] This invention of the frame buffer compression of the frame
buffer for display device manipulates this kind of situation by
combining the latest frame of image and the new object as shown in
FIG. 6. The latest frame 61 of image 62 being displayed is saved
into a frame buffer. The new object 63 with description of the
starting 64 and ending 65 positions of each line of pixels. The
position of the last pixel 66 will also be clearly identified. The
combined frame 71 of image will be looked like that shown in FIG.
7. All image pixels of the new object is inserted to the side of
the original object 72 with the corresponding position including
the starting, 74, and ending point, 75, of a line and the last
pixel 76.
[0034] FIG. 8 briefly illustrates the procedure of combining the
new object into the latest frame of image. Once the starting point
and ending point of each line of the new object is identified, the
corresponding segment of each line is calculated 81. Then, the
decompression unit recovers 82 the compressed segment of pixels to
the position of the end of the new object of each line, and
compressed then concatenates the combined pixel, then saves the
re-compressed line into the frame buffer for future use.
[0035] FIG. 9 illustrates details of an example of asserting an new
object into a frame of image and how this invention of frame buffer
compression for the display device operates on this situation. A
new object 95 is to be inserted into a line 90 of pixels comprising
several of segments 91, 92, 93, 94 of image data of an existing
frame which has been compressed and stored in a storage device. The
1.sup.st step is to calculate the staring and ending position of
the new object in which falls into this line and identifying the
corresponding segments of pixels which the new object to be
combined. In this example, the new object will be laid across Seg.
2 (Segment 2) and Seg. 3. And the next step is to decompress the
Seg. 2 and Seg. 3 till the corresponding position of the new object
pixels starts. Then, the part of the new object 98 belonging to
Seg. 2 concatenates with the recovered pixels of Seg. 2 and form an
updated new 96 Seg. 2. and the part of the new object 99 belonging
to Seg. 3 concatenates with the recovered pixels of Seg. 3 and form
an updated new 97 Seg. 3. Afterward, re-compressing 901, 902 the
updated Seg. 2 and updated Seg. 3. Other segments 904, 905 with
compressed pixels which don't include any pixel of the new object
are copied and concatenated with Seg.2 and Seg. 3 result in a
complete line 903 of compressed pixels.
[0036] FIG. 10 shows the block diagram of the implementation of
this invention of compressing the image frame buffer with new
object to be displayed on top of existing image. If the coming
pixels are within a complete frame, the image will be compressed
through a compression engine 101 which has most likely slower speed
of clock rate. A coming image is detected to tell whether this is a
new object 100 to be overlapped on top of the present image and
displayed jointly. Most lines of pixels within a new object have
either starting and ending or both address in the display frame
buffer different from previously displayed image. As described in
above paragraph of the method of inserting a new object into the
present frame to be displayed, the corresponding segment 103 of
previously compressed pixels will be recovered by extracting from
the frame buffer 106. The recovered corresponding segment of pixels
will then be concatenated 104 with the new object to be inserted
and re-compressed 105. The re-compressed segments will be
concatenated with those previously compressed segment and stored
into the frame buffer. The combined and compressed image frame
saved in the frame buffer will be decompressed 107 and sent to the
display device under the right timing. Since inserting a new object
into the existing frame buffer requires more procedure including
identifying the corresponding segments of new pixels fall into,
decoding the corresponding segments and re-compressing the
concatenated segments, using higher speed of the clock rate of
engines manipulating these functions helps in gaining higher
performance.
[0037] Further reducing the density of the frame buffer size of the
display device is feasible by applying smaller frame buffer size to
store only a partial of an image. For example, the image source 111
might reside in another device 116, a storage device 112 or
internet/networking device or a subsystem. A partial (a half, a
quarter or smaller part) frame 114 of an image is to be temporarily
stored in a image buffer within an LCD display driver. The
compression engine 113 compresses the coming pixels and stored into
the temporary image buffer 114. Another unit of decompression
engine 115 recovers the compressed pixels accessed from the
temporary image buffer 114 and sends to the source drivers to be
displayed in the display panel 118. In mobile devices like mobile
phone, digital camera, digital camcorder . . . there is DRAM to be
used as temporary buffer which is a candidate of storing the source
image to be displayed in the display panel. If the display driver
has an embedded function of converting YIUN or Y/Cr/Cb to R, G, B,
then this invention can also be applied to compress the image
source of YIUN or Y/Cr/Cb with similar procedure as described
above.
[0038] It will be apparent to those skills in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or the spirit of
the invention. In the view of the foregoing, it is intended that
the present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *